"""Reed Solomon error code calculation"""

__revision__ = "$Rev$"

# Factor table
factors = {
    5: (228, 48, 15, 111, 62),
    7: (23, 68, 144, 134, 240, 92, 254),
    10: (28, 24, 185, 166, 223, 248, 116, 255, 110, 61),
    11: (175, 138, 205, 12, 194, 168, 39, 245, 60, 97, 120),
    12: (41, 153, 158, 91, 61, 42, 142, 213, 97, 178, 100, 242),
    14: (156, 97, 192, 252, 95, 9, 157, 119, 138, 45, 18, 186, 83, 185),
    18: (83, 195, 100, 39, 188, 75, 66, 61, 241, 213, 109, 129,
         94, 254, 225, 48, 90, 188),
    20: (15, 195, 244, 9, 233, 71, 168, 2, 188, 160, 153, 145,
         253, 79, 108, 82, 27, 174, 186, 172),
    24: (52, 190, 88, 205, 109, 39, 176, 21, 155, 197, 251, 223, 155,
         21, 5, 172, 254, 124, 12, 181, 184, 96, 50, 193),
    28: (211, 231, 43, 97, 71, 96, 103, 174, 37, 151, 170, 53, 75, 34,
         249, 121, 17, 138, 110, 213, 141, 136, 120, 151, 233, 168, 93, 255),
    36: (245, 127, 242, 218, 130, 250, 162, 181, 102, 120, 84, 179, 220, 251,
         80, 182, 229, 18, 2, 4, 68, 33, 101, 137, 95, 119, 115, 44,
         175, 184, 59, 25, 225, 98, 81, 112),
    42: (77, 193, 137, 31, 19, 38, 22, 153, 247, 105, 122, 2, 245, 133,
         242, 8, 175, 95, 100, 9, 167, 105, 214, 111, 57, 121, 21,
         1, 253, 57, 54, 101, 248, 202, 69, 50, 150, 177, 226, 5, 9, 5),
    48: (245, 132, 172, 223, 96, 32, 117, 22, 238, 133, 238, 231, 205, 188,
         237, 87, 191, 106, 16, 147, 118, 23, 37, 90, 170, 205, 131, 88,
         120, 100, 66, 138, 186, 240, 82, 44, 176, 87, 187, 147, 160, 175,
         69, 213, 92, 253, 225, 19),
    56: (175, 9, 223, 238, 12, 17, 220, 208, 100, 29, 175, 170, 230, 192,
         215, 235, 150, 159, 36, 223, 38, 200, 132, 54, 228, 146, 218, 234,
         117, 203, 29, 232, 144, 238, 22, 150, 201, 117, 62, 207, 164, 13,
         137, 245, 127, 67, 247, 28, 155, 43, 203, 107, 233, 53, 143, 46),
    62: (242, 93, 169, 50, 144, 210, 39, 118, 202, 188, 201, 189, 143, 108,
         196, 37, 185, 112, 134, 230, 245, 63, 197, 190, 250, 106, 185, 221,
         175, 64, 114, 71, 161, 44, 147, 6, 27, 218, 51, 63, 87, 10,
         40, 130, 188, 17, 163, 31, 176, 170, 4, 107, 232, 7, 94, 166,
         224, 124, 86, 47, 11, 204),
    68: (220, 228, 173, 89, 251, 149, 159, 56, 89, 33, 147, 244, 154, 36,
         73, 127, 213, 136, 248, 180, 234, 197, 158, 177, 68, 122, 93, 213,
         15, 160, 227, 236, 66, 139, 153, 185, 202, 167, 179, 25, 220, 232,
         96, 210, 231, 136, 223, 239, 181, 241, 59, 52, 172, 25, 49, 232,
         211, 189, 64, 54, 108, 153, 132, 63, 96, 103, 82, 186)
}

# Galois Field log values
logval = (
    -255, 255, 1, 240, 2, 225, 241, 53, 3, 38, 226, 133, 242, 43,
    54, 210, 4, 195, 39, 114, 227, 106, 134, 28, 243, 140, 44, 23,
    55, 118, 211, 234, 5, 219, 196, 96, 40, 222, 115, 103, 228, 78,
    107, 125, 135, 8, 29, 162, 244, 186, 141, 180, 45, 99, 24, 49,
    56, 13, 119, 153, 212, 199, 235, 91, 6, 76, 220, 217, 197, 11,
    97, 184, 41, 36, 223, 253, 116, 138, 104, 193, 229, 86, 79, 171,
    108, 165, 126, 145, 136, 34, 9, 74, 30, 32, 163, 84, 245, 173,
    187, 204, 142, 81, 181, 190, 46, 88, 100, 159, 25, 231, 50, 207,
    57, 147, 14, 67, 120, 128, 154, 248, 213, 167, 200, 63, 236, 110,
    92, 176, 7, 161, 77, 124, 221, 102, 218, 95, 198, 90, 12, 152,
    98, 48, 185, 179, 42, 209, 37, 132, 224, 52, 254, 239, 117, 233,
    139, 22, 105, 27, 194, 113, 230, 206, 87, 158, 80, 189, 172, 203,
    109, 175, 166, 62, 127, 247, 146, 66, 137, 192, 35, 252, 10, 183,
    75, 216, 31, 83, 33, 73, 164, 144, 85, 170, 246, 65, 174, 61,
    188, 202, 205, 157, 143, 169, 82, 72, 182, 215, 191, 251, 47, 178,
    89, 151, 101, 94, 160, 123, 26, 112, 232, 21, 51, 238, 208, 131,
    58, 69, 148, 18, 15, 16, 68, 17, 121, 149, 129, 19, 155, 59,
    249, 70, 214, 250, 168, 71, 201, 156, 64, 60, 237, 130, 111, 20,
    93, 122, 177, 150)

# Galois Field antilog values
alogval = (
    1, 2, 4, 8, 16, 32, 64, 128, 45, 90, 180, 69, 138, 57,
    114, 228, 229, 231, 227, 235, 251, 219, 155, 27, 54, 108, 216, 157,
    23, 46, 92, 184, 93, 186, 89, 178, 73, 146, 9, 18, 36, 72,
    144, 13, 26, 52, 104, 208, 141, 55, 110, 220, 149, 7, 14, 28,
    56, 112, 224, 237, 247, 195, 171, 123, 246, 193, 175, 115, 230, 225,
    239, 243, 203, 187, 91, 182, 65, 130, 41, 82, 164, 101, 202, 185,
    95, 190, 81, 162, 105, 210, 137, 63, 126, 252, 213, 135, 35, 70,
    140, 53, 106, 212, 133, 39, 78, 156, 21, 42, 84, 168, 125, 250,
    217, 159, 19, 38, 76, 152, 29, 58, 116, 232, 253, 215, 131, 43,
    86, 172, 117, 234, 249, 223, 147, 11, 22, 44, 88, 176, 77, 154,
    25, 50, 100, 200, 189, 87, 174, 113, 226, 233, 255, 211, 139, 59,
    118, 236, 245, 199, 163, 107, 214, 129, 47, 94, 188, 85, 170, 121,
    242, 201, 191, 83, 166, 97, 194, 169, 127, 254, 209, 143, 51, 102,
    204, 181, 71, 142, 49, 98, 196, 165, 103, 206, 177, 79, 158, 17,
    34, 68, 136, 61, 122, 244, 197, 167, 99, 198, 161, 111, 222, 145,
    15, 30, 60, 120, 240, 205, 183, 67, 134, 33, 66, 132, 37, 74,
    148, 5, 10, 20, 40, 80, 160, 109, 218, 153, 31, 62, 124, 248,
    221, 151, 3, 6, 12, 24, 48, 96, 192, 173, 119, 238, 241, 207,
    179, 75, 150, 1)


def get_reed_solomon_code(data, num_code_words):
    """Calculate and return the Reed-Solomon error codewords
    of the given length, for the given data"""

    cw_factors = factors[num_code_words]
    code_words = [0, ] * num_code_words

    def gfsum(int1, int2):
        """Calculate the Galois field sum of two integers"""
        return int1 ^ int2

    def gfproduct(int1, int2):
        """Calculate the Galois field product of two integers"""
        if int1 == 0 or int2 == 0:
            return 0
        else:
            return alogval[(logval[int1] + logval[int2]) % 255]

    for data_word in data:

        tmp = gfsum(ord(data_word), code_words[-1])

        for j in range(num_code_words - 1, -1, -1):

            code_words[j] = gfproduct(tmp, cw_factors[j])

            if j > 0:
                code_words[j] = gfsum(code_words[j - 1], code_words[j])

    code_words.reverse()
    return ''.join([chr(code_word) for code_word in code_words])
